There have been many studies of methods that produce a sugar solution through hydrolysis of cellulose-containing biomass with cellulase, which uses little energy and is small in environmental load. However, the biggest problem of sugar solution producing methods using cellulase is the high manufacturing cost due to the high price of cellulase. Methods intended to recover and reuse cellulase after hydrolysis have been proposed to overcome such a technical drawback. However, there remains an issue of poor enzyme reusability attributed to the strong adsorption of cellulase to the hydrolysis residue generated during the hydrolysis of cellulose-containing biomass.
As methods that desorb the adsorbed cellulase from the hydrolysis residue to improve the cellulase recovery rate, a method that washes the hydrolysis residue with an alkaline aqueous solution of about pH 8 (D. E. Otter et al., “Elution of Trichoderma reesei Cellulase from Cellulose by pH Adjustment with Sodium Hydroxide,” Biotechnology Letters (1984), Vol. 6, No. 6, 369-374), a method that adds a nonionic surfactant to the hydrolysate of cellulose-containing biomass (JP-A-63-87994) and the like are known. On the other hand, as methods that reduce the adsorption of cellulase to the hydrolysis residue, a method that adds water-soluble salts during the hydrolysis of cellulose-containing biomass to adjust the electrical conductivity of reaction liquid to 5 to 25 mS/cm (Japanese Patent No. 4947223), a method that adds calcium carbonate particles in an amount of 1 to 10 weight % based on the solid weight of cellulose-containing biomass (JP-A-2012-100617) and the like are known.
As described above, there have been attempts to reduce cellulase use through recovery and reuse of the cellulase used in the hydrolysis of cellulose-containing biomass. However, the problem remains unsolved because of the low recovery rate due to the strong adsorption of the cellulase to the hydrolysis residue.
It could therefore be helpful to provide a method of producing a sugar solution with which cellulase can be more efficiently recovered.